BEIRUT — Syrian warplanes and artillery pounded opposition strongholds in Damascus and its suburbs Tuesday, as rebels in the northern city of Aleppo launched an operation to try to free hundreds of political detainees from the city’s central prison, activists said.
The fighting has escalated across Syria in recent weeks, particularly in Aleppo and Damascus, the country’s largest cities, as the rebels and President Bashar Assad’s regime try to gain the upper hand in the two-year-old conflict.
The Britain-based Syrian Observatory for Human Rights said some 6,000 people were killed nationwide in March alone, making it the deadliest month since the uprising began.
Fighting has also intensified in the southern provinces of Daraa and Quneitra, across from Jordan and the frontier with Israel.
On Tuesday, the Israeli military said a mortar shell exploded on its side of the frontier in the Golan Heights. The military said its soldiers returned the fire and recorded a direct hit. No other details were given.
The incident came after Israeli Defense Minister Moshe Yaalon visited the region Tuesday and warned that Israel would respond to any attack from Syria.
The escalation in the southern Quneitra region along the cease-fire line separating Syria from the Israeli-occupied Golan Heights accented concerns that Islamic extremists among the rebel forces could take over the front line opposite Israeli troops.
Damascus has become a key battleground in the civil war. From their strongholds in the suburbs, rebel fighters are trying to slowly push their way into the heart of the capital. Assad has deployed his most loyal and best equipped troops there, trying to insulate it from the violence.
The Observatory said government forces on Tuesday shelled the northern Damascus neighborhoods of Jobar, Barzeh, and Qaboun. It also reported an air raid on the suburb of Mleiha.
Maath al-Shami, an activist based in the suburb of eastern Ghouta, said there were several airstrikes in the area, which includes Mleiha. ‘‘Fighting is taking place on all fronts,’’ he said, referring to clashes east of Damascus.
‘‘Drones fly over eastern Ghouta then warplanes come and bomb the area,’’ Shami said, using his activist name because he feared government retribution.
State-run TV said rebels fired a mortar shell on the Damascus suburb of Muqailabiyeh, killing four people, including two children. It claimed troops killed scores of gunmen throughout the country.
The Observatory also reported that five people were killed, including a woman and an Iraqi national, when a barrage of mortar shells exploded in an area of the suburb of Jaramana, just few miles southeast of Damascus. The town is overwhelmingly proregime.
In Aleppo, rebels launched an attack dubbed ‘‘Freeing the Prisoners’’ that aims to eventually free detainees held in the city’s central prison, the Aleppo Media Center activist group reported.
Aleppo-based activist Mohammed Saeed said the operation is a three-pronged attack targeting at the Kindi Hospital, Ghondol square, and the central prison. He said the hospital has been turned into a military compound recently.